1. Field of the Invention
The present invention relates to communication control in a communication system in which a priority terminal is shorter than a non-priority terminal in a standby time.
2. Description of the Related Art
The previous allocation of wireless resources such as time and frequency used for transmission and reception in performing wireless communication between two apparatuses can be wasteful. For this reason, the IEEE 802.11 wireless LAN (hereinafter, referred to as “wireless LAN”), for example, uses a method of the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) in which transmission rights are acquired on a first-come-first-served basis if a carrier is not detected.
In a wireless LAN, inter frame space (IFS), which is a standby time until which own data can be transmitted after it is detected that the transmission of previous data is finished, is changed according to the kinds of data to avoid the collision of data, thereby preferentially transmitting ACK. Randomly setting a back-off time required before the start of data transmission (random back off) avoids the collision of data similar in priority.
Japanese Patent Application Laid-Open No. 2002-247051 discusses a technique in which the IFS is controlled to preferentially transmit a packet small in data size. Japanese Patent Application Laid-Open No. 2008-301075 discusses a technique in which a random back-off control is further improved to reduce the probability that a collision occurs.
In recent years, non-contact communication (proximity wireless communication) such as near field communication (NFC) and TransferJet (registered trademark) has appeared. The non-contact communication is very short in communication distance, and is controlled so that communicating apparatus are made close to each other in several centimeters (for example, 10 cm or less for NFC, or 3 cm or less for TransferJet) to establish a radio link, and the communicating apparatuses are kept away from each other to cut off the radio link.
In the TransferJet, it is assumed that the apparatuses perform data communication on a one-to-one basis with each other, and a white paper describing use cases is currently published (“TransferJet™ Overview Whitepaper” TransferJet Consortium, 2009). The white paper discloses that users make their apparatuses close to each other to enable sharing data.
For example, a method may be conceived in which a user performs an operation such as the selection of transmission data by its own apparatus and then brings it close to another apparatus to perform data communication for the purpose of sharing data using TransferJet. This is because it is difficult for the non-contact communication like the TransferJet to perform an operation such as the selection of transmission data with the connection of the radio link maintained because only a slight displacement of the apparatuses in the distance therebetween toward the outside of a communication range breaks the radio link therebetween.
The white paper does not deal with how the control of data transmission/reception is performed if both apparatuses are brought close to each other while selections of transmission data are completed in both apparatuses.
As a method for controlling data communication in that case, a method is conceived in which the CSMA/CA method is applied, as is the case with the wireless LAN, for example, to start data transmission on a first-come-first-served basis. However, in this case, until one apparatus previously acquiring transmission right finishes transmitting data, the other apparatus cannot transmit data.
If the other apparatus does not quickly start transmitting data, the user misjudges it as a failure in communication, and can perform unnecessary operations such as operating the apparatus or performing transmission operation again. If the transmission of data is not started even after a predetermined time period passes, it may be detected as a time-out error depending on the application of the other apparatus. If the amount of data in the apparatus previously acquiring transmission right is large in particular, such a problem probably occurs.